Field of the Invention
The present invention relates to a liquid crystal display device that performs backlight local dimming control.
Description of the Related Art
A liquid crystal display device is provided in a portable terminal such as a tablet terminal and a smartphone, a digital camera, a TV, and various monitors, in many cases. The liquid crystal display device includes a liquid crystal display panel in which liquid crystal elements with adjustable light transmittance are arranged to form a two-dimensional array, and a backlight that irradiates the liquid crystal display panel with light.
In recent years, there has been known a liquid crystal display device that includes a backlight unit capable of individually illuminating each of a plurality of segment areas into which a display area of the liquid crystal display panel is divided, and that performs backlight local dimming control (hereinafter referred to as BLD control) to independently control luminance of each of the segment areas. In the BLD control, if an image locally includes a dark section at low luminance and a bright section at high luminance, backlight luminance of a segment area corresponding to the dark section is reduced to reduce a misadjusted black level of the dark section. Accordingly, a contrast ratio of a display image displayed in a display area increases to improve image quality of the display image.
A liquid crystal display device that performed this kind of the BLD control (hereinafter simply referred to as liquid crystal display device) controls display luminance of each of segment areas by various methods in order to further improve the image quality of a display image. The “display luminance” called in the present specification is luminance to be observed from pixels (liquid crystal elements) of the liquid crystal display panel, and is determined by the product of transmittance of the pixels and the luminance of a backlight unit (referred to as backlight luminance).
In a liquid crystal display device described in Japanese Patent Application Laid-Open No. 2009-265671 (hereinafter referred to as PTL 1), as a range of a high luminance area displayed at high luminance in each of segment areas decreases, backlight luminance (display luminance) of the high luminance area is increased. As a result, for example, in a case where a night scene image acquired by photographing the moon in the night sky is displayed, it is possible to increase the backlight luminance of segment areas corresponding to the moon in the night scene image. Therefore, it is possible to increase a contrast ratio of the night scene image.
In a liquid crystal display device described in Japanese Patent Application Laid-Open No. 2012-008388 (hereinafter referred to as PTL 2), an upper limit value and a lower limit value of backlight luminance (display luminance) of each of segment areas are set, and a backlight unit is controlled so that the backlight luminance of each of the segment areas is within a range between the upper limit value and the lower limit value (refer to a portion (B) of FIG. 10). As a result, if an image including a white pattern in a part of a background, most of which is black, such as the night scene image described before is displayed, occurrence of a so-called “halo” caused by light of the backlight unit leaking to a periphery of the white pattern is prevented.
In a liquid crystal display device described in Japanese Patent Application Laid-Open No. 2011-158499 (hereinafter referred to as PTL 3), if the amount of light of a light source of each of segment areas is equal to or larger than a preset reference value based on brightness of an input image, the amount of light of each light source is reduced. As a result, during a scene change in which a display image changes from a high luminance image to a low luminance image, occurrence of an abnormal illumination state in which each light source illuminates a screen with unnatural brightness is prevented.